334 



MINERALOGY 



mineral when wet resembles ice in appearance. Crystals are 



cubelike in shape, with the corners and edges modified, while the 



massive mineral shows striations due to polysynthetic twinning. 



There is but one large deposit of cryolite in the world, that of 



FIG. 410. Cryolite Crystals from Ivigtut, Greenland. 



Ivigtut, West Greenland. This deposit is from 500 to 1000 feet 

 thick, occurring as a residual secretion in the granite ; associated 

 and contained in the cryolite are siderite, sphalerite, chalcopyrite, 

 galena, and other rare minerals, such as columbite, wolframite, 

 molybdite, and cassiterite. 



At Miask in the Urals and at the base of Pike's Peak in Colorado 

 other deposits occur, but these are small and of no commercial im- 

 portance. The product of the Greenland mine, some six or seven 

 thousand tons, is used in the manufacture of glass, porcelain, and 

 enamel ware. Cryolite forms the basis of the fused bath used as a 

 solvent for the oxide of aluminium in the Hall electrolytic process 

 for the reduction of the metal aluminium. 



Associated with cryolite, as a secondary product formed by the 

 substitution of calcium for some of the sodium, is pachnolite 

 (Na,Ca) 3 AlF 6 ,H 2 O. 



ATACAMITE 



Atacamite. CuCl 2 , 3 Cu(OH) 2 ; Basic chloride of copper ; 

 Cu = 14.9, Cl = 16.6, H 2 O = 12.7 ; Orthorhombic ; Type, Didig- 

 onal Equatorial ; a : b : c = .6612 : 1 : .7515 ; 100 A 110 = 33 

 28'; 001 A 101 = 48 49' ; 001 A 01 1 = 36 58'; Common forms, 



